On Friday, I was told that my Cartrack would be swopped on Monday at 8AM and I've made myself available

On Friday, I was told that my Cartrack would be swopped on Monday at 8AM and I've made myself available. After no one showed up I called and was told that it was scheduled for Tuesday. During the weekend I received an email stating I have an outstanding invoice. This morning (Monday) I get a call asking for debit order arrangements and I asked for it to be done tomorrow as the service was not done yet. I am being put under pressure for payment without any service delivery. Can't wait for my contract to finish.